Process for manufacture of tetraalkyllead and reclamation of by-product lead



3,452,069 PROCESS FOR MANUFACTURE OF TETRAALKYL- igil) AND RECLAMATION FBY-PRODUCT D Lawrence G. Cliver, Baton Rouge, La., assignor to EthylCorporation, New York, N.Y., a corporation of Virginia No Drawing. FiledJuly 29, 1966, Ser. No. 568,752 Int. Cl. C07f 7/26; C22b 13/02 US. Cl.260-437 11 Claims ABSTRACT OF THE DISCLOSURE Process for the productionof tetraalkyllead by the reaction of an alkyl chloride and a monosodiumlead alloy and the reclamation of by-product lead by admixing anamorphous carbon such as petroleum coke or calcined coke with thereactants, recovering the tetraalkyllead from the sludge, passing thesludge into a smelting furnace, and recovering molten lead from theresulting smelted sludge.

This invention relates to a process for the production of tetraalkylleadcompounds by the reaction of an alkyl chloride and a monosodium leadalloy and the reclamation of by-product lead by smelting sludge producedduring the reaction. More specifically, the present invention concernsthe use of amorphous carbon to lubricate the reaction and to aid in thesmelting operation.

Tetraethyllead has been produced for a number of years by reacting anexcess of ethyl chloride with a monosodium lead alloy. More recently,the production of tetramethyllead has begun in the same manner with theuse of methyl chloride instead of ethyl chloride. The reactionconditions of methyl chloride with the monosodium lead alloy of coursediffer somewhat from those of the reaction of ethyl chloride with thisalloy; however, both reactions are similar in that typically eachutilizes graphite as a lubricant in order to reduce the load onagitators used during the reactions. In these reactions, the sodium ofthe alloy is to the greatest part converted into sodium chloride; partof lead from the alloy is converted into tetraalkyllead; and thegreatest part of the remaining lead of the alloy is converted intometallic lead in a finely divided form.

After completion of the reaction, the excess of alkyl chloride isextracted by distillation (i.e. methyl chloride or ethyl chloride); thedistillation residue, or sludge, includes lead particles, whichconstitutes an important byproduct. The usual process for the recoveryof lead from the sludge containing lead as a by-product consists ofdrying the wet sludge in a continuously operating dryer in order toreduce the water content and subsequently smelting lead from the driedsludge in a reverberatory furnace.

The recovery of lead from the dried sludge in a single operation and bya practical process permitting a slag residue with a sufiiciently lowlead content so that it may be discarded without subjecting the slag toa new recovery operation is an old problem. The difiiculties are due tothe low melting rate of lead in the finely divided slurry, to thesolubility of impurities in lead at the furnace temperatures required tomelt the lead by-product, and to the fact that metallic lead does notseparate sharply from impurities. The use of such additives as petroleumcoke or calcined coke has thus been found to be of great benefit inrecovering lead in the smelting furnaces inasmuch as the coke promotesthe reduction of combined lead.

It is an object of the present invention to overcome the above noteddisadvantages of the prior art. It is a further object of the presentinvention to overcome the above noted disadvantages of the prior artthrough an eflicient States Patent 0 and economical combination process.It is a further object of this invention to increase the production oflead from smelting furnaces and reduce the slag rate while permittingefficient operation of the tetraalkyllead reaction agitators. Otheradvantages and objects of the present invention will become apparent inthe following descrip tion.

The present invention relates to a process for the production oftetraalkyllead by the reaction of an alkyl chloride and a monosodiumlead alloy and the reclamation of by-product lead by smelting sludgeproduced by the reaction. This reaction comprises providing an alkylchloride and a monosodium lead alloy and admixing therewith an amorphouscarbon material as a lubricant. The reaction takes place in the presenceof the amorphous carbon to produce a tetraalkyllead and a sludgecontaining amorphous carbon, unreacted lead and other compounds formedduring the reaction. Subsequent to the reaction, the tetraalkyllead isrecovered from the sludge and the remaining sludge is then passed into asmelting furnace. In the furnace the sludge is smelted to recover moltenlead with the amorphous carbon in the sludge then serving as a smeltingaid and additional amorphous carbon or other smelting aids may be addedif desired. The amorphous carbon in the reactants comprises from about0.5 percent to about 1.2 percent of the weight of the monosodium leadalloy. The reaction process is conducted at temperatures within therange of from about 122 F. to about 266 F. and the smelting process isconducted at a temperature within the range of from about 1000 F. toabout 2500* F.

The amorphous carbon of the present invention is of such consistencythat it is substantially volatile free within the temperature range ofthe reaction and substantially completely oxidized Within thetemperature range of the smelting. Amorphous carbons are commonly madeby heating organic matter to a moderately high temperature, either inthe absence of air or in the presence of a limited amount of air, untilthe organic matter is converted to carbon, and then heating with air,steam, carbon dioxide and the like. The term amorphous carbon is usedherein to mean carbons so made, including those made directly fromanimal or vegetable materials, such as Wood, nut shells and bones whileretaining their original structures, as well as those made fromunorganized organic substances, such as sugar and extracted lignin. Twoamorphous carbons preferred in the practice of the present invention arepetroleum coke and calcined coke.

The amorphous carbons of the present invention may be of any size andshape since agitation of the reactants during the reaction processserves to grind the carbon to the proper size and shape. However, it isgenerally preferred that the carbon be particulate. And, it is mostpreferred that the individual carbon particles average about A inch indiameter.

The substitution of amorphous carbon for graphite has several advantagesincluding, first, amorphous carbon provides good lubrication in thereaction apparatus and is reactive in the lead recovery furnaces topromote the reduction of combined lead; in contrast, graphite isinactive, tends to interfere with efficient furnace operation andincreases the amount of slag produced during operation of the furnaces;second, amorphous carbon is one of the additives in the recovery furnaceand introduction of amorphous carbon through lead sludge allows bettermixing of the sludge and the carbon and a reduction in the carbonrequired for efficient furnace operation. An added benefit is thatamorphous carbon is much less expensive than graphite.

Having thus briefly set forth the invention, the following is a moredetailed description thereof.

Tetraethyllead is manufactured by the present invention through reactingan excess of ethyl chloride with lead monosodium alloy. Tetramethylleadis similarly mannfactured employing methyl chloride in place of ethylchloride. Both these manufacturing processes are well known and may benoted in numerous publications. For example, the commercial manufactureof tetramethyllead may be found in US. Patent 3,049,558.

In the tetramethyllead reaction a lubricant is highly desirable and ithas been common prior to this invention to utilize graphite for thatpurpose. On the other hand, in the tetraethyllead reaction lubricationis not nearly so necessary. Therefore, little if any lubricant is used.Hence, while the present invention is applicable to both the manufactureof tetraethyllead and tetramethyllead, it is more preferably used in themanufacture of tetramethyllead. The following description is drawntherefore more specifically to operations involved with tetramethyllead.

The present invention utilizes amorphous carbon bot-h as a lubricantduring the lead alkyl forming reaction and as a smelting aid during thesubsequent smelting operation. The amorphous carbon must be of such aquality that it gives off substantially no volatile materials at thetemperature of the lead alkyl forming reaction which is conducted at atemperature of from about 122 F. to about 266 F. Also, the amorphouscarbon must burn at a temperature no greater than the temperature of thesmelting operation which ranges from about 1000 F. to about 2500 F.

In the present invention an autoclave is charged with monosodium leadalloy, preferably as flakes, in the proportion of approximately 50pounds per cubic foot of reaction space. In addition, from about 0.5percent to about 1.2 percent by weight, based upon the amount of thealloy, of amorphous carbon is introduced as a reaction lubricant. Thisamorphous carbon later serves as a smelting aid. Additionallyapproximately 0.2 percent of aluminum, as methyl aluminumsesquichloride, may be introduced. Toluene, in proportions of aboutpercent of the alloy weight may be further introduced. The reactor andcontents are heated to approximately 176 F., and a feed of liquid methylchloride is then started at a rate of about 10 parts per minute per 100parts of alloy charge. The reaction occurs promptly and is shown by asignificant rise in operating temperature. The pressure is allowed torise to approximately 180 p.s.i.g. and at this time refiux of vapor,principally methyl chloride, is initiated to maintain the pressure atthis level. Temperature of the reacting mixture is controlled in therange of about 176 F. to about 203 F. by variation of the degree ofcooling for refluxing purposes. The methyl ohloride feed is continueduntil a total of approximately 35 pounds by weight per 100 pounds byWeight of alloy charge has been introduced, this corresponding toapproximately 160 percent excess of the theoretical requirement. Thereaction conditions are continued for several hours after termination offeed, and then the temperature stops rising and begins to drop slightly.The excess pressure is vented shortly thereafter and the auoclavecontents cooled to approximately ambient temperatures. The charge isthen discharged from the autoclave into a pool of water in a steamdistillation vessel, and the tetramethyllead and toluene are recoveredin high yield. The remaining reaction mass, which is referrcd to as wetsludge, is Water sluiced to a water filled pit. This reaction masscontains the amorphous carbon which will subsequently serve as asmelting aid during the smelting operation.

The wet sludge is removed from the water filled pit by a crane andplaced in a hopper from which it is fed by a screw feeder to acontinuously operating dryer. It is then processed in the dryer toreduce the Water content to a value of 6 percent or less. From thedryer, substantially dried sludge fiows by gravity to a dry hopper andis then screw fed into a furnace for smelting.

The furnace employed for the smelting process is a 4 reverberatoryfurnace, and the heat required for the smelting operation is preferablysupplied by forced air natural gas burners. The heat supplied by theburners maintains the furnace temperature at from about 1600" F. toabout 2500 As the sludge is melted, the level of lead increases andduring smelting additional smelting aids such as coke and soda ash orothers may be added if desired. When the maximum lead level is obtained,molten lead is removed from the furnace by means of gravity flow throughlead run lines. Typically, this operation is repeated approximatelyevery hour. Molten lead from the furnace flows into a heated vessel forweighing and purification. Slag, which results from the smeltingoperation is removed (from the furnace on the average of about every 8hours. During the smelting operation the amorphous carbon is burned offhaving served its function as a smelting aid.

To further illustrate the operation of the present invention, thefollowing examples illustrative typical results.

EXAMPLE L-EFFEGT OF COKE AND SODA ASH ON LEAD RECOVERY FROM TML SLUDGECONTAINING GRAPHITE Lead Slag rate Graphite rod. (lbjcwt. Coke Soda ashFeed Source (lb. day) Pb) (lb/day) (lb./day) charge) TML l Sludge M 8. 2367 860 20 Do M 7. 4 0 0 20 EXAMPLE IL-EFFECT OF SUBSTITUTION OF COKEFOR GRAPHITE ON LEAD RECOVERY FROM TML SLUDGE 1 Tetrametliyllead.

It is clear from the above examples that graphite introduced during thereaction as a lubricant is inactive, tends to interfere with efiicientfurnace operation and increases the amount of slag produced during theoperation of the furnaces Whereas the use of amorphous carbon as asubstitute for graphite not only promotes lubrication of the reactionbut aids in recovery of lead during the smelting operation.

It will be understood that while there have been given herein certainspecific examples of the practice of this invention, it is not intendedthereby to have this invention limited to or circumscribed by thespecific details of materials, proportions, or conditions hereinspecified, other than where explicitly stated, in view of the fact thatthis invention may be modified according to individual perferences orconditions without necessarily departing from the spirit of thedisclosure and the scope of the appended claims.

1 claim:

1. A process for the production of tetramethyllead by the reaction ofmethyl chloride and a monosodium lead alloy and the reclamation ofby-product lead by smelt ing sludge produced by said reaction,comprising in combination,

(A) providing reactants comprising methyl chloride and a monosodium leadalloy;

(B) admixing an amorphous carbon selected from the group consisting ofpetroleum coke and calcined coke with said reactants,

(C) reacting said reactants in the presence of said amorphous carbonadmixed therewith at a temperature of from about 122 F. to about 266 F.to produce tetraalkyllead and sludge containing said amorphous carbon,

(D) recovering said tetramethyllead from said sludge,

( E) passing said sludge to a smelting furnace,

(F) smelting said sludge containing said amorphous carbon at atemperature of from about 1000 F. to about 2500 F.,

(G) recovering molten lead from the resulting smelted sludge.

2. The process of claim 1 further characterized by the addition ofaluminum to said reactants.

3. The process of claim 2 further characterized by the aluminum beingadded as methylaluminum sesquichloride.

4. The process of claim 1 further characterized by the addition oftoluene, in proportions of about percent of the alloy Weight, to saidreactants.

5. The process of claim 1 further characterized by said amorphous carbonbeing admixed in an amount comprising from about 0.5 percent to about1.2 percent of the weight of said monosodium lead alloy.

6. The process of claim 1 further characterized by said amorphous carbonbeing substantially volatile free within the temperature range of saidreaction and substantially completely oxidized within the temperaturerange of said smelting.

7. The process of claim 6 further characterized by said amorphous carbonbeing praticulate.

8. The process of claim 7 further characterized by the particulateamorphous carbon comprising particles being about inch in diameter.

9. The process of claim 6 further characterized by the further additionof smelting the sludge.

aids just prior to smelting 10. The process of claim 9 furthercharacterized by the smelting aid being soda ash.

11. The process of claim 9 further characterized by the smelting aidbeing amorphous carbon.

References Cited UNITED STATES PATENTS 1,975,171 10/ 1934 Parmelee260437 2,004,160 6/ 1935 Downing et a1. 260 -437 2,407,551 9/1946 Heron260437 2,407,262 9/ 1946 lLlIlCh 260437 2,661,361 12/1953 Grandjean 2437 2,763,673 9/1956 Gittins et al. 260-437 2,765,328 10/1956 Padgitt260-437 2,853,378 9/1958 Mattison 260-437 XR 2,971,967 2/1961 Anderson260437 3,049,558 8/1962 Cook et a1 260-437 1,827,820 10/1931 Kirsebom 78XR 1,950,387 3/19-34 Betterton et a1. 7578 2,007,545 7/1935 Monson 75782,692,197 10/ 1954 Denison 7578 2,823,113 2/1958 Porro et a1. 7577 XR2,834,669 5/ 1958 Pendar 7577 3,052,535 9/ 1962 Peters 7577 3,188,1996/1965 Mattison 757'8 XR TOBIAS E. LEVOW, Primary Examiner. H. M. S.SNEED, Assistant Examiner.

U .8. Cl. X.R. 7577

